For example, Patent Documents 1 and 2 disclose a wireless power supply system that wirelessly supplies electric power from a storage battery installed in an underwater vehicle to a storage battery installed in an underwater facility. Since oxygen cannot be supplied from the surroundings under water unlike on the ground, an underwater vehicle often uses a storage battery (such as a lithium ion battery, a nickel hydrogen battery, or a lead storage battery) as a power source.
The term “wireless” in such a wireless power supply system means that an electric power transmission wire of a power-transmitter does not directly contact with an electric power transmission wire of a power-receiver, and does not mean that a structure in which one of the power-transmitter and the power-receiver is installed is not in contact with a structure in which the other of the power-transmitter and the power-receiver is installed. For stable transmission of electric power, it is desirable that the positional relationship between the power-transmitter and the power-receiver be fixed. Accordingly, as disclosed in Patent Documents 1 and 2, both structures are firmly fitted and fixed to each other during the transmission of electric power.